The present invention relates to a central processing unit of a modular programmable controller with a communications interface. The central processing unit includes a processor unit, a memory device, a peripheral interface, and a programming interface, all interconnected with a bus system.
In the case of a central processing unit of a modular programmable controller, the programming interface is designed as a point-to-point interface, so that a programming unit, e.g.,a programming terminal or a PC, can be connected via an interface cable to the central processing unit. To network the central processing units of a plurality of controllers of this type, modular programmable controllers have their own communication modules with two interfaces. The one interface can be coupled via an interconnecting cable to the programming interface of the central processing unit. The other interface has bus capability, so that the communication module is connectable to a bus, e.g.,to the SINEC H1 or to the SINEC L2.
There are several disadvantages entailed by this configuration. First, space is needed for the communication module. Also, the communication module is often more expensive than the central processing unit itself. In addition, the communication between the communication module and the central processing unit is interference-prone and slow. Data transfer rates of up to 1.5 MBaud (SINEC L2) or of up to 10 MBaud (SINEC H1), for example, can be realized over the bus, while the data transfer rate over the interconnecting cable merely amounts to 9.6 kBaud.
EP-A-0 540 903 discloses a control module having a network interface. The application program, inter alia, can be loaded via the network interface into the control module.
A programmable controller having an interface with bus capability is known from the WO-A-91 14988. However, this interface is not used as a programming interface.
Modular programmable controllers consist not only of the central processing unit, but also of at least one peripheral unit, mostly of a plurality of peripheral units. In particular, when the peripheral units are designed as intelligent peripheral units, it may be desirable to have the peripheral units communicate with other units outside of the programmable controller.